There currently exist different ways of carrying out the control of a wind farm composed of a variable number of wind turbine generators.
On the one hand it is possible to carry out individual control of the different wind turbine generators, in which case each generator incorporates a local controller supervising the levels of voltage, current, etc. in the generator terminals.
Nevertheless, these magnitudes are not controlled at the wind farm level, and this can give rise to breaches of the requisites imposed by the network.
In any case, this solution can be suitable in wind farms with a small number of wind turbine generators, owing to the high cost of having central control in a substation compared to the total cost of the facilities.
One example of that control, applied to the particular case of frequency control, is described in patent EP 1 282 774. In it is described the control of a turbine which adapts the active power that it generates, as a function of the frequency measurements made in the terminals of the generator, with the aim of contributing towards restoring the frequency of the network in the event of any deviations of it above or below the permitted limits.
On the other hand, more widespread is the use of a central control unit controlling the global magnitudes necessary for guaranteeing the correct integration into the wind farm network. It is usual to locate that control unit in the electrical substation housing the transformer and the rest of the equipment necessary to transfer the energy generated by the wind farm to the electrical network.
Nevertheless, this solution also presents a series of drawbacks such that it requires additional equipment, but also, in the event of that equipment failing, the central control is rendered inoperative.
The patent application EP 1 467 463 is a good example of this control scheme and in it is described the mode of operation of a wind farm, in which the central control unit sends the necessary instructions to each wind turbine generator in the farm, depending on the frequency of the network.
The most common thing is that, as well as said central controller, each wind turbine generator incorporates its own control in order to thereby ensure the operation within the limits of that generator, in such a way that the patent application EP 1 512 869 describes a central controller which calculates the reactive power instructions for each wind turbine generator as a function of the voltage of the farm and an individual control in each wind turbine generator originates the particular voltage instruction for that reactive power demanded from the central control.
In this case, if a failure occurs in the central control, the reactive power instruction can be erroneous with regard to the global voltage control when the operating conditions in the network change. Nevertheless, it incorporates the advantage compared to the previous option that, as a result of the individual controls that are incorporated, the voltage levels in the terminals of each wind turbine generator are supervised so that, though they might not be optimum for control over the wind farm voltage, at least they do not exceed the permitted limits.
The patent application US 2002029097 A1 discloses a centralized control system for a wind farm composed of several wind turbine generators.
The patent application US 2002013805 A1 discloses a network of computers or of nodes which communicate with each other according to a protocol that can be of the token passing type.